Gavialosuchus

Gavialosuchus
Skull of Gavialosuchus eggenburgensis in the Krahuletz Museum in Eggenburg ( Lower Austria )
Temporal occurrence
Eggenburgium
20.5 to 18.5 million years
Locations
Burgschleinitz formation from Eggenburg ( Lower Austria )
Systematics
Sauropsida Archosauria Crocodiles (crocodilia) Gaviale (Gavialidae) Tomistominae Gavialosuchus
Scientific name
Gavialosuchus
Toula & Kail , 1885
Art
Gavialosuchus eggenburgensis

Gavialosuchus is an extinct genus of crocodiles with a gavial - like elongated (longirostriner) snout from the group of Tomistominae . Gavialosuchus eggenburgensis is the type species and at the same time the only generally recognized representative of the genus. Fossil finds come from the Burgschleinitz Formation (Lower Miocene - Eggenburgian , about 18.5 to 20.5 million years ago) in the vicinity of Eggenburg in Lower Austria .

Etymology and history of research

The generic name is made up of the term “ Gavial ” for longirostrine crocodiles and the Latinized form (“ suchus ”) for the ancient Greek name Σοῦχος (“ Souchos ”) of the Egyptian crocodile god Sobek . The additional species " eggenburgensis " refers to the location near Eggenburg. The species name can roughly be translated as "Gavial crocodile von Eggenburg".

For the construction of the Franz-Josefs-Bahn from Vienna to Cheb (Eger) between 1866 and 1872, numerous gravel and sand pits were operated for the extraction of building material, including in the area around Eggenburg. Both the railway construction site itself and the associated dismantling were regularly visited by Johann Krahuletz to look for artifacts and fossils. In one of these sand pits in Schindergraben on the western slope of the Kalvarienberg near Eggenburg, Krahuletz found not only bone remains of the manatee Metaxytherium krahuletzi , which was later named after him, but also the fragments of a badly broken crocodile skull .

Toula and Kail succeeded in reassembling the individual fragments into an almost complete skull. The two used gutta-percha as an adhesive. The experience that Toula was able to gain with the adhesive later benefited him when reconstructing the skull of the Hundsheim rhinoceros . Krahuletz insisted that the original fossils should remain in Eggenburg and turned down offers to buy. However, he allowed the production of plaster casts and the Viennese scientists had to be satisfied with that.

Franz Toula , 1882

The first description of the genus and type species was carried out in 1885 by Toula and Kail already under the name Gavialosuchus eggenburgensis or under the name Crocodilus (Gavialosuchus) eggenburgensis . For the diagnosis , the authors used comparative material from three recent species ( Nile crocodile , Sunda gavial and Ganges gavial ) that had been made available to them by Andreas Kornhuber , Carl Brühl and Franz Steindachner from various Viennese zoological collections. Toula and Kail saw the Sunda-Gavial ( Tomistoma schlegelii ) as the most closely related recent species. The first description was presented on May 7, 1885 at a meeting of the "Mathematical-Natural Science Class" of the Imperial Academy of Sciences in Vienna. The results of these meetings, which took place weekly at the time, were published regularly in the "Anzeiger der Kaiserliche Akademie der Wissenschaften". In issue 11 of the year 1885 there is already a short version of the first description with a summary of the most important results, but without images. The actual first description was not published until later in the same year. In September 1885 appeared in "The Annals and Magazine of Natural History", an even more abridged summary in English.

In November 1885 Richard Lydekker gave a lecture that was published in 1886 and in which he synonymized the newly established genus Gavialosuchus with the genus Tomistoma . At the time when Lydekker was writing his lecture, only the short version of the first description of Gavialosuchus eggenburgensis and its even shorter English translation were available to him. In the publication that appeared in the following year, however, he mentions in a follow-up, dated January 20, 1886, that in the meantime he had had the opportunity to examine the corresponding images from the actual first description and that the opinion he had already expressed was fully confirmed. Perhaps in response to this writing, Toula gave one of the plaster casts he had made to the British Museum of Natural History , where Lydekker was active at the time, as a gift in 1886 .

North American forms such as "Gavialosuchus" carolinensis are now assigned to the genus Thecachampsa .

In 1915, Elias Howard Sellards described an apparently similar species from the Miocene of Florida as Tomistoma americana . Charles C. Mook assigned the taxon in 1921 as Gavialosuchus americana of the genus Gavialosuchus and referred explicitly to the first description by Toula and Kail. With Gavialosuchus carolinensis , another North American species was introduced into the genus in 1996 by Bruce R. Erickson and Glen T. Sawyer .

A short time later, however, the first doubts arose as to whether an assignment of the North American forms to the genus Gavialosuchus was permissible. In 2000, Gavialosuchus eggenburgensis was included for the first time in more extensive phylogenetic analyzes and there were first indications that the North American forms with Gavialosuchus eggenburgensis do not form a monophyletic group . Albert C. Myrick, Jr. synonymized Gavialosuchus americana in 2001 with the taxon Thecachampsa antiqua described by Joseph Leidy in 1852 , but initially hardly met with approval from experts. It wasn't until 2007 that Myrick's assessment was confirmed by Piras et al. partially confirmed. Gavialosuchus americana and Gavialosuchus carolinensis were placed next to Thecachampsa antiqua in the genus Thecachampsa . Later phylogenetic analyzes confirmed this classification and Gavialosuchus eggenburgensis was again the only known representative of the now monotypic genus Gavialosuchus .

Synonyms

The eventful history of research and the general difficulty of systematically classifying fossil representatives of the crocodiles is reflected in the number of synonyms for Gavialosuchus eggenburgensis used in the specialist literature . The references given in the following list only refer to the sources given in the individual references and accordingly represent a subjective selection.

• Crocodilus eggenburgensis
• Crocodilus (Gavialosuchus) eggenburgensis
• Gavialosuchus eggenburgense
• Gavialosuchus eggenburgensis
• Tomistoma eggenburgense
• Tomistoma eggenburgensis

Fossil record

In addition to the skull, painstakingly reconstructed by Toula and Kail, the fossil material recovered by Krahuletz also includes an isolated single tooth and several vertebrae , of which only one presacral vertebra is, however, well-preserved to show diagnostically useful features.

features

Original images of the skull of Gavialosuchus eggenburgensis from the first description by Toula & Kail, 1885

Panel I: View of the skull from above

Panel II: Fig. 1. View of the skull from below; Fig. 2. View of the skull from the left side

The Sunda Gavial ( Tomistoma schlegelii ) is the most closely related recent species.

The skull of Eggenburg, without the missing tip of the snout, reaches a length of 73 cm and its dimensions correspond approximately to those of the largest gharial ( Gavialis gangeticus ) which can reach a length of up to 6 m. The shape of the skull, however, corresponds to that of the Sunda Gavial ( Tomistoma schlegelii ). In particular, the transition from the skull to the elongated snout is fluid, as in the Sunda gavial and not separated, as in the gharial.

The characteristics listed below correspond to the first description by Toula and Kail, which was essentially also used for later phylogenetic analyzes. The listed characteristics are a selection and mainly relate to differences to the recent Sunda Gavial and the closely related fossil form Tomistoma lusitanica from the Miocene of the Mediterranean area according to the phylogenetic data matrix used by Stéphane Jouve 2016. Abbreviations used in the text refer to the original images from the first description reproduced on the right.

Features common to Tomistoma lusitanica as opposed to Sunda Gavial

The table-like top of the skull is flat and not recessed in the middle as in the Sunda-Gavial. The incisive foramen ("fi.") Is narrow and occupies less than half the width of the premaxilla . In the Sunda Gavial, this opening is extremely reduced and thin. The upper temporal window ("ft.") Is wider than it is long. The rear edge of the upper temporal window is straight and oriented laterally backwards. In addition, the rear edge of the upper temple window is thinner than the side edge. In the recent Sunda-Gavial, the upper temple window is rather small and rounded with a clearly thickened rear edge compared to the side edge. The anterior tip of the praefrontal bone ("fa.") Lies entirely between the nasal bone ("na.") And the tearbone ("la."). In the Sunda Gavial, this bone ends in an indentation within the nasal bone. The frontal bone ("f.") Ends approximately at the same level as the paired praefrontal bone ("fa."). In T. lusitanica it can sometimes protrude well beyond it, but in Sunda Gavial it always ends behind it.

Crocodiles have a closable outer ear canal , which prevents water from entering while diving. The muscles responsible for the closing mechanism are located in a recess on the scale leg . In the Sunda Gavial the edges of this depression are oriented parallel to each other, in G. eggenburgensis and T. lusitanica they are widened towards the front.

Distinguishing features from Tomistoma lusitanica and Sunda Gavial

The fourth tooth of the maxilla is most pronounced; in Tomistoma lusitanica and the Sunda-Gavial it is the fifth tooth. The maxilla ("sm.") Has a backward protruding process that engages between the tearbone ("la.") And the nasal bone ("na."). The Sunda-Gavial has a similar process, which, however, occupies a corresponding indentation within the tearbone. In Tomistoma lusitanica there is no comparable process of the maxilla. The medial hemicondyle of the quadratum is small and bent backwards in the abdomen. In T. lusitanica and the Sunda gavial it is more extensive. The ploughshare is completely covered by the maxilla and palatine bone ("pal."). In T. lusitanica and the Sunda Gavial it is partially exposed. A bony pillar (“prefrontal pillar”) extending anteriorly from the pre-frontal bone is narrow in its dorsal half and not widened along the longitudinal axis of the skull as in T. lusitanica and the Sunda gavial. The lateral edge of the zygomatic bone ("ju.") Rises laterally to the postorbital clasp and laterally forms a base for the postorbital clasp. In T. lusitanica and the Sunda Gavial, however, a furrow separates this edge from the postorbital clasp.

Systematics and phylogeny

Tomistominae  Kentisuchus spenceri     Dollosuchoides densmorei     Megadontosuchus arduini     Tomistoma cairensis     Thecachampsa americana     Thecachampsa antiqua     Thecachampsa carolinense     Penghusuchus pani     Paratomistoma courti     Tomistoma petrolica     Toyotamaphimaea machikanensis     Gavialosuchus eggenburgensis     Tomistoma lusitanica     Tomistoma schlegelii

Systematic position of Gavialosuchus eggenburgensis within the Tomistominae according to Brochu & Storrs, 2012;

Tomistominae  Maroccosuchus zennaroi     Kentisuchus spenceri     Kentisuchus astrei     Megadontosuchus arduini     Dollosuchoides densmorei     Thecachampsa antiqua     Thecachampsa carolinensis     Toyotamaphimaea machikanensis     Penghusuchus pani     "Tomistoma" cairense     Paratomistoma courti     "Tomistoma" coppensi     Tomistoma schlegelii     Gavialosuchus eggenburgensis     Tomistoma lusitanica

Systematic position of Gavialosuchus eggenburgensis within the Tomistominae according to Jouve, 2016;

The systematic classification of fossil crocodiles is extremely complex. This is not only due to the fact that there is often only fragmentary evidence of fossil representatives, but also because the relationships between the recent forms have not been completely clarified. Phylogenetic analyzes based on purely morphological aspects partly contradict the results of molecular genetic studies.

This applies in particular to the relationships between the gharial ( Gavialis gangeticus ) and the Sunda gavial ( Tomistoma schlegelii ) and thus indirectly also the systematic position of Gavialosuchus . According to the classical, purely morphological systematics, the Gharial and its fossil relatives ( Gavialidae / Gavialinae ) and the Sunda gavial and its fossil relatives ( Tomistominae ) are not closely related. The latter are counted among the real crocodiles (Crocodylidae), while the former are compared to the Brevirostres (Crocodylidae + Alligatoridae ) as an independent group .

The molecular genetic studies show, however, that gharial and sunda gavial are closely related species and, taking into account the fossil forms, Tomistominae and Gavialinae together form the order of the Gavialidae which is more closely related to the Crocodylidae than to the Alligatoridae.

The two adjacent cladograms show the hypotheses most frequently cited in the literature on the internal systematics of the fossil tomistominae. What both have in common is that Gavialosuchus eggenburgensis , Tomistoma lusitanica and the recent Sunda gavial lie in a common clade , while the North American forms ( Thecachampsa ) , which used to belong to the genus Gavialosuchus, also form an apparently well-developed, independent clade apart.

Both cladograms differ significantly from one another in some details and both show some deficiencies in the systematics of the fossil tomistominae. Both analyzes place different fossil representatives of the genus Tomistoma , to varying degrees, together with representatives of other genera in several clades or partial clades. According to the analysis by Brochu & Storrs , 2012, the genus Tomistoma should be described as polyphyletic ; according to the analysis by Jouve , in 2016 at least as paraphyletic . Jouve partly takes this fact into account by placing the generic names of the Tomistoma representatives apart from the clade Gavialosuchus eggenburgensis + Tomistoma lusitanica + Tomistoma schlegelii under quotation marks.

The analysis by Brochu & Storrs shows Tomistoma lusitanica to be most closely related to the Sunda gavial, with which the taxon forms a common partial clade, which is opposed to a second partial clade with Gavialosuchus eggenburgensis and the East Asian taxon Toyotamaphimaea machikanensis . At least this does not contradict the retention of an independent genus for Gavialosuchus eggenburgensis .

Jouve's analysis, however, shows Tomistoma lusitanica to be closest related to Gavialosuchus eggenburgensis , with which the taxon forms a common partial clade, with the Sunda gavial as a sister taxon. Strictly speaking, either Tomistoma lusitanica would have to be incorporated into the genus Gavialosuchus or, as already proposed by Lydekker in 1886, Gavialosuchus eggenburgensis would have to be integrated into the genus Tomistoma .

Paleecology

According to the shape of the skull, Gavialosuchus eggenburgensis was probably piscivor .

The sediments of the Burgschleinitz Formation were deposited in a shallow bay (“Eggenburger Bucht”) on the western edge of the Paratethys . The bay encroached far into the land areas of the Bohemian Massif and was part of a richly indented coastal region with numerous islands, peninsulas, bays and estuaries . According to Krahuletz, Toula & Kail already described a connection between the discovery of Gavialosuchus eggenburgensis and a conspicuous location of coarse crystalline rocks . Such locations are widespread within the Burgschleinitz Formation, are mostly related to larger finds of vertebrate remains and, according to modern analyzes , are interpreted as deposits of debris flows , possibly triggered by severe storm events.

The coastal region itself and its hinterland wore a dense vegetation cover, which is approximately at the same time locally to the formation of thin brown coal - seams led ( Mold formation ). In open waters (fresh and brackish water ) algae (including Botryococcus braunii ) and evening primrose plants of the genus Ludwigia occurred. Silting areas near the banks were shaped by spawning herbs , sour grasses and hedgehog cobs . In the adjacent Moor societies dominated mosses, Cyperaceae, and grasses with heather-like from the family of Cyrillaceae and bog myrtle plants of the genus Myrica . Swamp forests were of hickory trees , Tupelobäumen and various representatives of Taxodiaceae coined in the lowland forests dominated pines , ash trees (similar to white ash ), maples , alders , birches , willows , Rautengewächse the genus Toddalia and other representatives of evening primrose plants. Away from the swamps occurred forests with walnut crops of Engelhardia / oreomunnea group and the genus Juglans , Mastixiaceen , elm , linden , beech plants of the genera Castanea and Castanopsis , heather-like the genus Symplocos and Sapotengewächsen and entwined forming vine plants of the genus parthenocissus . The mountain relief in the further hinterland was supported by coniferous forests with hemlocks , pines and umbrella firs . Pine trees could also have formed an integral part of the immediate coastal forests.

The plant community can be assigned to the neogene pollen zone NGZ II of the central Paratethys and speaks for a very warm climate with high humidity all year round.

Gavialosuchus eggenburgensis shared this habitat among other manatees the type Metaxytherium krahuletzi and dolphin Schizodelphis sulcatus addition there are numerous examples of sharks, rays, bone fish and turtles. The Anthracothere Brachyodus onoideus and various small mammals such as Amphiperatherium , Prolagus , Heteroxerus , Melissiodon or Ligerimys have been found in land mammals .

Individual evidence

1. ↑ ^{a b c d e f g h i j k l m n o p q} F. Toula & JA Kail: About a crocodile skull from the tertiary deposits of Eggenburg in Lower Austria - A paleontological study. In: Memorandum of the Imperial Academy of Sciences - mathematical and natural science class , Volume 50, pp. 299–355, 1885. (digitized version )
2. ↑ ^{a b c d e} P. Pervesler, R. Roetzel & A. Uchman: Ichnology of Shallow Sublittoral Siliciclastics of the Burgschleinitz Formation (Lower Miocene, Eggenburgian) in the Alpine-Carpathian Foredeep (NE Austria). In: Austrian Journal of Earth Sciences , Vol. 104, No. 1, pp. 81–96, 2011. (digitized version)
3. ^ ^{A b} F. Toula: The rhinoceros of Hundsheim. Rhinoceros (Ceratorhinus osb.) Hundsheimensis nov. form. With remarks on the proportions of eleven skulls of Rhinoceros (Ceratorhinus) sumatrensis. In: Treatises of the Imperial Geological Institute , Volume XIX, Issue 1, pp. 1–92, 1902. (digitized version )
4. ↑ ^{a b c d} F. Toula & JA Kail: About a crocodile skull from the tertiary deposits of Eggenburg in Lower Austria. In: Anzeiger der Kaiserliche Akademie der Wissenschaften - Mathematisch-Naturwissenschaftliche Classe , XXII. Year 1885, No. 11, pp. 107-109, 1885. (digitized version)
5. ^ ^{A b c} F. Toula & JA Kail: On a Crocodile.skull from the Tertiary Deposits of Eggenburg in Lower Austria. In: The Annals and Magazine of Natural History , Vol.XVI, Series 5, No. 93, p. 236, 1885. (digitized version)
6. ^ ^{A b c} R. Lydekker: On the Occurrence of the Crocodilian Genus Tomistoma in the Miocene of the Maltese Islands. In: The Quarterly Journal of the Geological Society of London , Vol. 42, pp. 20–22, 1886. (digitized version)
7. ↑ ^{a b} R. Lydekker: Catalog of the Fossil Reptilia and Amphibia in the British Museum (Natural History) - Part I. P. 63, Taylor & Francis, London, 1888. (digitized version)
8. ↑ EH Sellards: A New Gavial from the Late Tertiary of Florida. In: The American Journal of Science , Vol. 40, Series 4, pp. 135-138, 1915. (digitized version)
9. ^ ^{A b} C. C. Mook: Skull Characters and Affinities of the Extinct Florida Gavial Gavialosuchus americana (Sellards). In: Bulletin of the American Museum of Natural History , Vol. XLIV, pp. 33–41, 1921. (digitized version )
10. ^ BR Erickson & GT Sawyer: The estuarine crocodile Gavialosuchus carolinensis n. Sp. (Crocodylia: Eusuchia) from the late Oligocene of South Carolina, North America. In: Monograph of the Science Museum of Minnesota , Vol. 3, 47 pp., 1996.
11. ↑ ^{a b c} Ch. A. Brochu: Phylogenetic Relationships and Divergence Timing of Crocodylus Based on Morphology and the Fossil Record. In: Copeia , Volume 2000, No. 3, pp. 657–673, 2000. (digital copy )
12. ↑ ^{a b} Ch. A. Brochu & Ph. D. Gingerich: New Tomistomine Crocodylian from the Middle Eocene (Bartonian) of Wadi Hitan, Fayum Province, Egypt. In: Contributions from the Museum of Paleontology - The University of Michigan , Vol. 30, No. 10, pp. 251–268, 2000. (digitized version )
13. ↑ AC Myrick, Jr .: Thecachampsa antiqua (Leidy, 1852) (Crocodylidae: Thoracosaurinae) from Fossil Marine Deposits at Lee Creek Mine, Aurora, North Carolina, USA. In: Smithsonian Contributions to Paleobiology , No. 90, pp. 219-225, 2001.
14. ↑ ^{a b} P. Piras, M. Delfino, L. Del Favero & T. Kotsakis: Phylogenetic position of the crocodylian Megadontosuchus arduini and tomistomine palaeobiogeography. In: Acta Palaeontologica Polonica , Vol. 52, No. 2, pp. 315–328, 2007. (digitized version )
15. ↑ ^{a b c d e f} Ch. A. Brochu & GW Storrs: A Giant Crocodile from the Plio-Pleistocene of Kenya, the Phylogenetic Relationships of Neogene African Crocodylines, and the Antiquity of Crocodylus in Africa. In: Journal of Vertebrate Paleontology , Vol. 32, No. 3, pp. 587–602, 2012. (digitized version )
16. ↑ ^{a b c d e f g h i j k l m n o p q r s} St. Jouve: A new basal tomistomine (Crocodylia, Crocodyloidea) from Issel (Middle Eocene; France): palaeobiogeography of basal tomistomines and palaeogeographic consequences. In: Zoological Journal of the Linnean Society , Vol. 177, pp. 165–182, 2016. (online)
17. ↑ Ch. Depéret: About the fauna of miocene vertebrates from the first Mediterranean stage of Eggenburg. In: Meeting reports of the mathematical and natural science class of the Imperial Academy of Sciences , Volume 104, pp. 395-416, 1895. (Digitized version)
18. ↑ ^{a b c d} P. Pervesler, R. Roetzel & O. Mandic: Siren deposits in the marine shallow water deposits of the Eggenburg Bay (Burgschleinitz Formation, Eggenburgian, Lower Miocene). In: Geologische-Paläontologische Mitteilungen - University of Innsbruck , Volume 23, pp. 87-103, 1998. (digitized version )
19. ↑ O. Abel: Life pictures from the animal world of the past. 643 pp., Published by Gustav Fischer, Jena, 1922. (digitized version)
20. ↑ JR Oaks: A time-calibrated species tree of Crocodylia reveals a recent radiation of the true crocodiles. In: evolution. Vol. 65, No. 11, pp. 3285–3297, 2011. doi: 10.1111 / j.1558-5646.2011.01373.x (digitized version )
21. ↑ FF Steininger & R. Roetzel: Geological basics, lithostratigraphy, biostratigraphy and chronostratigraphic correlation of the molasses sediments on the eastern edge of the Bohemian mass. In: R. Roetzel (Ed.): Geology on the eastern edge of the Bohemian Massif in Lower Austria. Focus on sheet 21 horn. Working conference of the Federal Geological Institute, Eggenburg, pp. 102–108, 1991. (digitized version )
22. ↑ ^{a b} I. Draxler: The submiocene microflora from the Eggenburg-Horn-Geras area. In: R. Roetzel (Ed.): Geology on the eastern edge of the Bohemian Massif in Lower Austria. Focus on sheet 21 horn. Workshop of the Federal Geological Institute, Eggenburg, pp. 109–113, 1991. (digitized version )
23. ↑ P. Mein: The small mammal fauna of the Lower Miocene (Eggenburgia) from Maigen, Lower Austria. In: Annals of the Natural History Museum in Vienna , Volume 90, Section A, pp. 49–58, 1989. (digitized version)

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